658
Effect of strategic ration balancing with use of Prolak and MetaboLys on the efficiency of milk protein production and environmental impact
The objective of this study was to evaluate the effect of reduced dietary CP concentration on efficiency of N utilization and environmental impact in a commercial dairy herd. The general herd diet was reformulated with the Agricultural Modeling and Training System model and use of Prolak and MetaboLys. Reformulation reduced the dietary CP concentration (17.4 vs 15.9 %) and resulted in a DCAD of 31.3 vs 21.2 mEq/100 g DM. Cows were completely randomized to two groups with 155 cows each and milked three times per day, and the two groups had the same average days in milk (DIM=149) prior to initiation of the study. Respective diets were fed in a 40 d switch back design trial with two periods. Milk weight, milk and manure samples were obtained at the end of the second and third week of each period. The manure samples were incubated in closed chambers for 19 d to measure ammonia (NH3) flux. Average pen DMI was similar (25.1 vs 25.3 kg/d). The reformulated diet supported 0.6 kg less milk production (44.3 vs 43.7±0.16kg/d), less milk protein yield (1.27 vs 1.25±0.01kg/d) and the same amount of fat yield (1.48 vs 1.46 ±0.01kg/d), but increased the ratio of true protein/total CP intake (28.4 vs 30.6%) and milk CP/total CP intake (33.3 vs 38.6%). The concentration of MUN was lower for cows fed the reformulated diet (13.4 vs 11.56 mg/dl). When the cows were fed reformulated diet, they consumed 9% less N, produced 1% less milk N, but excreted 14% less predicted urinary N and 15.4% less calculated fecal N. The manures from the reformulated diet had a lower NH3 flux (147 vs 137mg*h-1*m-2). This study illustrated that the lower N diet could improve the efficiency of N utilization and reduced the environmental impact, but may influence the milk production.
Keywords: milk protein, lysine, rumen undegradable protein